Tự điển Food Science, Technology And Nutrition - Vần U,V,W

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485 tion, 2 = toxin produced in host without adherence, 3 = toxin pro- duced in host with adherence to cells, 4 = toxin produced by inva- sive bacteria, 5 = toxin produced by bacteria causing systemic infection; type of toxin: 1 = enterotoxin, 2 = neurotoxin, 3 = non- protein toxin; target or mechanism of action; individual toxin number. Shown as TX x.x.x.x. Tyndall effect Dispersion of light by a colloidal suspension (see colloid), commonly determined as turbidity by measuring the light emitted at 90 ° to the direction of incident light. typhoid Gastrointestinal infection caused by Salmonella typhi, transmitted by food or water contaminated by faeces of patients or asymptomatic carriers. Paratyphoid is due to S. paratyphi. tyramine The amine formed by decarboxylation of the amino acid tyrosine; chemically p-hydroxyphenylethylamine. tyrosinase See phenol oxidases. tyrosine A non-essential amino acid, abbr Tyr (Y), Mr 181.2, pKa 2.43, 9.11, 10.13 (—OH), codons UAPy. Can be formed from the essential amino acid phenylalanine, hence it has some sparing action on phenylalanine. In addition to its role in proteins, tyrosine is the precursor for the synthesis of melanin (the black and brown pigment of skin and hair), and for adrenaline and noradrenaline. tyrosinosis genetic disease due to lack of p-hydroxyphenylpyru- vate oxidase (EC 1.13.11.27), affecting the metabolism of tyro- sine and leading to excretion of p-hydroxyphenylpyruvate in the urine. Treatment is by restriction of dietary intake of pheny- lalanine and tyrosine. tzatziki Greek; grated cucumber in yogurt, ﬂavoured with garlic, olive oil and vinegar. U ubichromenol Cyclised derivatives of ubiquinones. ubiquinones Coenzymes in the respiratory (electron transport) chain in mitochondria, also known as coenzyme Q or mito- quinones; widely distributed in nature. Chemically, derivatives of benzoquinone with isoprene side chains. There is no evidence that they are dietary essentials; they may have antioxidant activity. ucuhuba butter A yellow solid fat obtained from ucuhuba nuts, the fruit of Myristica surinamensis. 90% saturated, 7% mono- unsaturated, 3% polyunsaturated, vitamin E 0.6 mg/100 mL. udon Japanese; ﬁne transparent noodles made from wheat. UFA Unesteriﬁed fatty acids, see fatty acids, non-esteriﬁed.
486 ugli citrus fruit; cross between grapefruit and tangerine, also called tangelo (USA); ﬁrst produced in Jamaica in 1930. UHT See ultra-high-temperature sterilisation. UL Tolerable upper intake level of a nutrient; maximum intake (from supplements and enriched foods) that is unlikely to pose a risk of adverse effects on health. ulcer A crater-like lesion of the skin or a mucous membrane result- ing from tissue death associated with inﬂammatory disease, infec- tion or cancer.Peptic ulcers affect regions of the gastrointestinal tract exposed to gastric juices containing acid and pepsin: gastric ulcer in the stomach and duodenal ulcer in the duodenum. Treatment was formerly conservative, with a bland diet, fol- lowed if necessary by surgery. Now treated by inhibition of gastric acid secretion using histamine receptor antagonists or inhibitors of the proton pump. May be caused or exacerbated by infection with Helicobacter pylori. ulcerative colitis See colitis. ullage Air space left in cask or bottle after some liquid has been removed. ultracentrifuge See centrifuge. ultraﬁltration Procedure for removal of low molecular weight compounds from plasma, protein solutions, etc., using a semipermeable membrane and either hydrostatic pressure or centrifugation. ultra-high-temperature sterilisation (UHT) Sterilisation at higher temperatures and for shorter times, than high-temperature short-time sterilisation. ultrasound Sound above the normal range of human hearing, commonly above 20 kHz. ultraviolet (UV) irradiation Light of wavelength below the visible range. Wavelength for maximal germicidal action is 260 nm; poor penetrating power and of value only for surface sterilisation or sterilising air and water. Also used for tenderis- ing and ageing of meat, curing cheese, and prevention of mould growth on the surface of bakery products. Ultraviolet from sun- light is responsible for skin tanning, and the formation of vitamin d from 7-dehydrocholesterol in the skin. umami Name given to the special taste of monosodium gluta- mate, some other amino acids, protein and the ribonucleotides (inosinate and guanylate). The Japanese name for a savoury ﬂavour, now considered one of the ﬁve basic senses of taste. umbles Edible entrails of any animal (especially deer) which used to be made into pie, umble pie or humble pie. uncoupling proteins Proteins in mitochondria that act to uncou- ple the processes of electron transport and oxidative phospho-
487 rylation, so permitting more or less uncontrolled oxidation of metabolic fuels, with production of heat. An important part of maintenance of body temperature by non-shivering thermogen- esis, and maintenance of energy balance; they are stimulated by leptin. UCP-1 (thermogenin) is the best studied. It occurs in brown adipose tissue (see adipose tissue, brown), and is activated by free fatty acids produced in response to β-adrenergic stimulation. UCP-2 occurs in a variety of tissues, including skeletal muscle and lung; UCP-3 occurs only in skeletal muscle. uncrystallisable syrup See syrup. unesteriﬁed fatty acids (UFA) See fatty acids, non-esteriﬁed. UNICEF United Nations Children’s fund; web site http://www.unicef.org/. universal product codes (UPC) Standard multidigit numbers that represent product, size, manufacturer and nature of contents, on food and other labels as machine-readable bar codes. unsaponiﬁable See non-saponiﬁed. unsaturated fatty acids See fatty acids. UNU United Nations University; web site http://www.unu.edu/. UPC See universal product codes. uperisation A method of sterilising milk by injecting steam under pressure to raise the temperature to 150 °C. The added water is evaporated off. uracil A pyrimidine; see nucleic acids. urataemia High blood concentration of uric acid and its salts, as in gout. uraturia Urinary excretion of high concentrations of uric acid and its salts. urd bean See grams, indian. urea CO(NH2)2, the end-product of nitrogen metabolism in most mammals, excreted in the urine. Synthesised in the liver from ammonia (arising from the deamination of amino acids) and the amino acid aspartic acid. It is the major nitrogenous compound in urine, and the major component of the non-protein nitrogen in blood plasma. urease Intestinal bacterial enzyme (EC 3.5.1.5) that hydrolyses urea to ammonia and carbon dioxide. Important in the entero- hepatic cycling of urea. Also found in some beans. urethane Ethyl carbamate, used as intermediate in organic syn- theses, as a solubiliser and as the precursor for polyurethane foam. Found in small amounts in liqueurs made from stone fruits, wines and some distilled spirits where it is formed by reaction between alcohol and nitrogenous compounds; cause for concern since it is genotoxic, and hence a potential carcinogen.
488 uric acid The end-product of purine metabolism in human beings and other apes; most other mammals have the enzyme uricase (EC 1.7.3.3), which oxidises uric acid to allantoin, which is more soluble in water. gout is the result of excessive formation of uric acid, and/or impaired excretion; it is only slightly soluble in water, and in excess it crystallises in joints, as gouty nodules (tophi) under the skin and sometimes in the kidney. urobilinogen Pigment in urine derived from the bile pigments, which, in turn, are formed from haemoglobin. When urine is left to stand, the urobilinogen is oxidised in air to urobilin. urogastrone Name given to a peptide found in urine that inhibits gastric secretion, (nearly) identical to epidermal growth factor. urwaga See orubisi. USDA US Department of Agriculture, created as an independent department in 1862; web site http://www.usda.gov/. USRDA reference intakes used for nutritional labelling of foods in the USA before the introduction of daily values. uszka Polish; type of ravioli, egg-ﬂour dough stuffed with mushrooms. UV See ultraviolet. V vacherin (1) Circular cakes of meringue and cream. (2) French mild cheeses made from cow’s milk; traditionally moulded in ﬂat circles and wrapped in a border of bark. vac-ice process Alternative name for freeze drying. vacreation deodorisation of cream by steam distillation under reduced pressure; developed in New Zealand. vacuum contact drying Or vacuum contact plate process, a method of drying food in a vacuum oven in which the material is heated by hot plates both above and below. As the material shrinks due to water loss, continuous contact is maintained by closing the plates; heats the food more effectively than a simple vacuum oven. vada Indian; spiced, deep fried balls of legume ﬂour that has been left overnight to undergo a lactic acid bacterial fermentation, together with Leuconostoc mesenteroides, which produces carbon dioxide as a leavening agent. vagotomy Surgical cutting of part of the vagus (10th cranial) nerve, usually to reduce secretion of acid and pepsin by the gastric mucosa. valerian Extracts and the essential oil of the herbaceous peren- nial Valeriana ofﬁcianalis are used as ﬂavouring in many foods.
489 The root has traditionally been used as a sedative and tranquil- liser, with evidence of efﬁcacy. valgus Any deformity that displaces the hand or foot away from the mid-line of the body; e.g. genu valgus is knock knees, as seen in rickets. See also varus. validity Of an assay, the extent to which a method measures what it purports to measure. See also accuracy; precision; sensitivity; speciﬁcity. valine An essential amino acid, abbr Val (V), Mr 117.1, pKa 2.29, 9.74, codons GUNu; rarely, if ever, limiting in foods. valzin, valzol See dulcin. vanadium A mineral known to be essential to experimental animals, although sufﬁciently widespread for human dietary deﬁ- ciency to be unknown. Its precise function is unknown, although it acts as an activator of a number of enzymes. vanaspati Indian; puriﬁed hydrogenated vegetable oil; similar to margarine and usually fortiﬁed with vitamins A and D. Also used to prepare ghee (vanaspati ghee). vanilla Extract of the vanilla bean, fruit of the tropical orchid Aracus (or Vanilla) aromaticus and related species. Discovered in Mexico in 1571 and could not be grown elsewhere, because pollination could be effected only by a small Mexican bee, until artiﬁcial pollination was introduced in 1820. Main growing regions now Madagascar and Tahiti. The major ﬂavouring principle is vanillin (chemically methyl protocatechuic aldehyde), but other substances present aid the ﬂavour. Ethyl vanillin is a synthetic substance which does not occur in the vanilla bean; 3.5 times as strong in ﬂavour, and more stable to store than vanillin, but does not have the true ﬂavour. vanillin See vanilla. VaporPrintTM imaging A graphical representation of the ﬂavour proﬁle obtained using a znoseTM ‘electronic nose’. variety meat American name for offal. varus Any deformity that displaces the hand or foot towards the mid-line of the body; e.g. genu varus is bow legs, as seen in rickets. See also valgus. vasoactive intestinal peptide (VIP) Protein secreted by the pancreas; over-secretion can cause severe diarrhoea. vasoconstriction Constriction of the blood vessels; the reverse of vasodilatation. vasodilatation (vasodilation) Dilation of the blood vessels; the reverse of vasoconstriction. Caused by a rise in body tempera- ture; serves to lose heat from the body.
490 vasopressin Antidiuretic hormone secreted by the pituitary; acts to increase resorption of water in the kidneys and to constrict blood vessels. VCD See vacuum contact drying. VDP Volatile decomposition products. veal Meat of young calf (Bos taurus) 21/2–3 months old. Composition/100 g: water 76 g, 456 kJ (109 kcal), protein 20.3 g, fat 2.5 g (of which 42% saturated, 42% mono-unsaturated, 16% polyunsaturated), cholesterol 84 mg, carbohydrate 0 g, ash 1.1 g, Ca 17 mg, Fe 0.9 mg, Mg 25 mg, P 213 mg, K 331 mg, Na 83 mg, Zn 3.5 mg, Cu 0.1 mg, Se 8.8 µg, vitamin E 0.3 mg, B1 0.09 mg, B2 0.29 mg, niacin 7.4 mg, B6 0.45 mg, folate 13 µg, B12 1.5 µg, pantothenate 1.3 mg. A 100 g serving is a source of Se, vitamin B2, a good source of P, Zn, vitamin B6, pantothenate, a rich source of niacin, vitamin B12. vegans Those who consume no foods of animal origin. See vegetarians. VegemiteTM Australian; yeast extract. vegetable See fruit. vegetable butters See cocoa butter equivalents; cocoa butter substitutes. vegetable oyster See salsify. vegetable pepsin See papain. vegetable protein products General term to include textured soya and other bean products, often made to simulate meat (see tex- tured vegetable protein). The basic material is termed ﬂour when the protein content is not less than 50%; concentrate, not less than 65%; isolate, not less than 90% protein. vegetable spaghetti See spaghetti squash. vegetarians Those who do not eat meat or ﬁsh, either for ethical/religious reasons or because they believe that a meat-free diet confers health beneﬁts. Apart from a risk of vitamin b12 deﬁ- ciency, there are no adverse effects of a wholly meat-free diet, although vegetarian women are more at risk of iron deﬁciency than those who eat meat. Vitamin B12 is found only in meat and meat products, but supplements prepared by bacterial fermenta- tion (and hence ethically acceptable to the strictest of vegetari- ans) are available. The strictest vegetarians are vegans, who consume no products of animal origin at all. Those who consume milk and milk prod- ucts are termed lacto-vegetarians; those who also eat eggs, ovo- lacto-vegetarians. Some vegetarians (pescetarians) will eat ﬁsh, but not meat; demi-vegetarians eat little or no meat, or eat poultry but not red meat. veitchberry Variety of loganberry. veltol See maltol.
491 venison Meat of deer (Odocoileus spp.); traditionally game, but now mainly farmed. Composition/100 g: water 74 g, 502 kJ (120 kcal), protein 23 g, fat 2.4 g (of which 43% saturated, 33% mono-unsaturated, 24% polyunsaturated), cholesterol 85 mg, carbohydrate 0 g, ash 1.2 g, Ca 5 mg, Fe 3.4 mg, Mg 23 mg, P 202 mg, K 318 mg, Na 51 mg, Zn 2.1 mg, Cu 0.3 mg, Se 9.7 µg, vitamin E 0.2 mg, K 1.1 mg, B1 0.22 mg, B2 0.48 mg, niacin 6.4 mg, B6 0.37 mg, folate 4 µg, B12 6.3 µg, A 100 g serving is a source of Se, Zn, vitamin B1, B6, a good source of Cu, Fe, P, a rich source of vitamin B2, niacin, B12. venting Removal of air from a retort or retort pouch before heating. verbascose A non-digestible tetrasaccharide, galactosyl- galactosyl-glucosyl-fructose, found in legumes; fermented by intestinal bacteria and causes ﬂatulence. verbena A lemon ﬂavoured herb, the leaves of Lippia citroidora. verdoﬂavin Name given to a substance isolated from grass, later shown to be riboﬂavin (vitamin b2). verjuice Literally green juice; sour juice of crab apples (and sometimes unripe grapes) formerly used in cooking meat, ﬁsh and game dishes. Now normally replaced by lemon juice. vermicelli See pasta. vermicide Any drug used to kill or expel intestinal parasitic worms. vermouth Fortiﬁed wine (about 16% alcohol by volume) ﬂavoured with herbs and quinine. French vermouth is dry and colourless; Italian may be red or white and is sweet. Drunk as an apéritif, either with soda or with gin or vodka (when called a martini). Name originally derived from German Wermut for wormwood, a toxic ingredient that was included in early ver- mouths (as in absinthe). Sweet or Italian vermouth, 15–17% alcohol (by volume), 12–20% sugar (by weight). Dry or French type 18–20% alcohol, 3–5% sugar. VerseneTM Ethylenediamine tetra-acetic acid, see edta. VervTM Calcium stearyl-2-lactate, used to reduce baking varia- tions in ﬂour. It produces a more extensible dough, more easily machined, and gives a loaf with better keeping properties and more uniform structure. vervain Herb (Verbena ofﬁcianilis) used to make herb tea. very low-density lipoproteins (VLDL) See lipoproteins, plasma. vetch Old term applied generally to legumes; originally Vicia spp., also called tares. ve-tsin See monosodium glutamate. Vibrio cholerae The causative agent of cholera, bacterium trans- mitted especially through water; forms an enterotoxin after
492 adhering to epithelial cells in gut. Infective dose 108 organisms, onset 2–5 days, duration 4–6 days, TX 3.1.2.2. vichyssoise Leek and potato cream soup, served cold. vicilin Globulin protein in pea and lentil. vicine One of the toxins in broad beans, responsible for acute haemolytic anaemia or favism. victory bread American; recipe for bread containing soya ﬂour to spare wheat, in a circular published by the US Secretary of Agri- culture in 1918. Vienna ﬂour Specially ﬁne ﬂour used to make strudel pastry, Vienna bread and cakes. Viennese coffee Ground coffee containing dried ﬁgs. viili Finnish; yogurt made using Streptococcus cremoris as the main organism. villi, intestinal Small, ﬁnger-like processes covering the surface of the small intestine in large numbers (20–40/mm2), projecting some 0.5–1 mm into the lumen. They provide a surface area of about 300 m2 for the absorption of nutrients from the small intestine. See also gastrointestinal tract. vinasses The residual liquors from sugar beet molasses; contain appreciable quantities of betaine. vinegar A solution of acetic acid (not less than 4%); the product of two fermentations, ﬁrst with yeast to convert sugars into alcohol; this liquor, called gyle (6–9% alcohol), is then fermented with Acetobacter spp. to form acetic acid. In most countries vinegar is made from grape juice (wine vinegar, may be from red, white or rosé wine). vinegar, balsamic Made from grape juice that has been concen- trated over a low ﬂame and fermented slowly in a series of wooden barrels; traditionally made only around Modena, Italy. vinegar, cider Made from apple juice, and known simply as vinegar in the USA. vinegar, malt Made from malted barley and may be distilled to a colourless liquid with the same acetic acid content but a more mellow ﬂavour. vinegar, non-brewed (or non-brewed condiment) A solution of acetic acid, 4–8%, coloured with caramel. vinegar, rice Made from saké. vine leaves Leaves of the grape vine, Vitis vinifera, used in Mediterranean cuisine. Composition/100 g: (edible portion 95%) water 73 g, 389 kJ (93 kcal), protein 5.6 g, fat 2.1 g (of which 20% saturated, 7% mono-unsaturated, 73% polyunsaturated), carbohydrate 17.3 g
493 (6.3 g sugars), ﬁbre 11 g, ash 1.6 g, Ca 363 mg, Fe 2.6 mg, Mg 95 mg, P 91 mg, K 272 mg, Na 9 mg, Zn 0.7 mg, Cu 0.4 mg, Mn 2.9 mg, Se 0.9 µg, vitamin A 1376 µg RE (18 579 µg carotenoids), E 2 mg, K 108.6 mg, B1 0.04 mg, B2 0.35 mg, niacin 2.4 mg, B6 0.4 mg, folate 83 µg, pantothenate 0.2 mg, C 11 mg. viniﬁcation The process of fermentation of sugars in grape juice to make wine. viosterol Irradiated ergosterol; vitamin d2. VIP See vasoactive intestinal peptide. Virginia date See persimmon. VirolTM A vitamin preparation based on malt extract. virpa See sowans. viscera The organs within a body cavity, used especially for the abdominal viscera, liver, spleen, gastrointestinal tract, kidneys, etc. viscoelastic Material such as cheese, dough or gelled food, that has both viscous and elastic properties (see viscosity); when a shear stress is removed it does not return to its original shape, but is deformed. viscogen Thickening agent for whipping cream. Two parts of lime (calcium oxide) in six parts of water, added to ﬁve parts of sugar in ten parts of water; used at the rate of 3–6 g/L of cream. viscometer Instrument for measuring the viscosity of liquids. viscosity Of a liquid or gas, its resistance to ﬂow. Decreases with increasing temperature for liquids, but increases for gases. Dynamic viscosity is the ratio of shear stress : shear rate. Kinematic viscosity is dynamic viscosity/density. See also dilatant; plastic ﬂuids; pseudoplastic; reynolds number; rheopectic; thixotropic; viscoelastic. viscosity, dynamic (or absolute) The ratio of shear stress : shear rate for ﬂuids that exhibit a linear relationship between shear stress and shear rate (Newtonian ﬂow). vision The process of vision is mediated by photosensitive pig- ments formed by reaction between retinaldehyde (vitamin a aldehyde) and the protein opsin. The pigments are known vari- ously as visual purple (because of its colour), rhodopsin (in the rod cells of the retina) and iodopsin (in the cone cells, with sen- sitivity to different wavelengths of light in different cells). Expo- sure to light results in bleaching of the pigment, with loss of the retinaldehyde and a conformational change in the protein, which leads to closure of a sodium channel in the retinal cell, and ini- tiation of a nerve impulse. visual pigments, visual purple See vision. vitafoods Foods designed to meet the needs of health-conscious
494 consumers that enhance physical or mental quality of life and may increase health status. vitamers Chemical compounds structurally related to a vitamin, and converted to the same active metabolites in the body. They thus possess the same kind of biological activity, although some- times with lower potency. When there are several vitamers, the group of compounds exhibiting the biological activity of the vitamin is given a generic descriptor (e.g. vitamin a is the generic descriptor for retinol and its derivatives as well as several carotenoids). vitamin There are 13 organic compounds (thus excluding trace minerals) essential to human life in very small amounts. Eleven of these must be supplied in the diet (vitamins A, B1, B2, B6, B12, C, E, K, folic acid, biotin and pantothenic acid); two (niacin and vitamin d) can be made in the body if there is sufﬁcient of the amino acid, tryptophan, and sunlight, respectively. The word may be pronounced either veitamin or vittamin. Vitamins A, D, E and K are grouped together as fat-soluble vitamins, because they are soluble in lipids, but not in water. Vitamin C and the B vitamins (including pantothenic acid, biotin and folic acid) are grouped together as the water- soluble vitamins since they are all soluble in water, but not lipids. vitamin A (see p. 495) Fat-soluble vitamin, occurring either as the preformed vitamin (retinol) found in animal foods or as a pre- cursor (carotenes) found in plant foods. Required for control of growth, cell turnover and fetal development, maintenance of fer- tility and maintenance of the normal moist condition of epithe- lial tissues lining the mouth and respiratory and urinary tracts; essential in vision. The main active metabolites in the body are retinaldehyde, all-trans- and 9-cis-retinoic acids. Deﬁciency leads to slow adaptation to see in dim light (poor dark adaptation), later to night blindness; then drying of the tear ducts (xerophthalmia) and ulceration of the cornea (ker- atomalacia) resulting in blindness. The vitamin A content of foods is expressed as retinol equivalents, i.e. retinol plus carotene; 1 µg retinol = 6 µg β- carotene = 12 µg other active carotenoids = 3.33 international units. See also conjunctival impression cytology; relative dose response test; retinol binding protein; vision. vitamin A toxicity Retinol in excess of requirements is stored in the liver, bound to proteins, and is a cumulative poison. When the storage capacity is exceeded, free retinol causes damage to cell membranes. carotene is not toxic in excess, since there is only a limited capacity to form retinol from carotene.
495 VITAMIN A The recommended upper limits of habitual daily intake of retinol are about 12.5 × reference intake for adults, but only 2.5 × reference intake for infants. Retinol is also teratogenic in excess, and for pregnant women the recommended upper limit of daily intake is 3000–3300 µg. vitamin A2 Old name for dehydroretinol, the form found in livers of freshwater ﬁsh; has 40% of the biological activity of retinol. vitamin B complex Old-fashioned term for the various B vitamins: vitamin b1 (thiamin), vitamin b2 (riboﬂavin), niacin, vitamin b6, vitamin b12, folic acid, biotin and pantothenic acid. These vitamins occur together in cereal germ, liver and yeast; function as coenzymes; and historically were discovered by sep- aration from what was known originally as ‘vitamin B’; hence, they are grouped together as the B complex. vitamin B1 Thiamin. Thiamin diphosphate is a coenzyme in metabolism of glucose, and in the citric acid cycle. Thiamin triphosphate has a role in nerve conduction, by activating a chlo- ride channel. Deﬁciency, especially when associated with a carbohydrate-rich diet, results in the disease beriberi, degenera- tion of the sensory nerves in the hands and feet, spreading through the limbs, with ﬂuid retention and heart failure. Rela- tively acute deﬁciency, especially associated with alcohol abuse,
496 results in central nervous system damage, the wernicke– korsakoff syndrome. See also thiochrome; transketolase. VITAMIN B1 vitamin B1 dependency syndromes A very small number of chil- dren have been reported with a variant form of maple syrup urine disease in which the defect is in the binding of thiamin diphosphate to the branched chain keto acid dehydrogenase (EC 1.2.4.4). These children respond well to supplements of large amounts of vitamin B1, without the need for strict control of their intake of the amino acids. vitamin B2 Riboﬂavin. Coenzyme in a wide range of oxidation reactions of fats, carbohydrates and amino acids, as riboﬂavin phosphate (ﬂavin mononucleotide), ﬂavin adenine dinucleotide or covalently bound riboﬂavin at the active site of the enzyme. Riboﬂavin-dependent enzymes are collectively known as ﬂavoproteins. Deﬁciency impairs energy-yielding metabolism and results in a group of symptoms known as ariboﬂavinosis, including crack- ing of the skin at the corners of the mouth (angular stomatitis), ﬁssuring of the lips (cheilosis) and tongue changes (glossitis); seborrhoeic accumulations appear around the nose and eyes. Not fatal because there is very efﬁcient recycling of riboﬂavin in deﬁciency. See also glutathione reductase; lumichrome; lumiﬂavin. VITAMIN B2
497 vitamin B3 Term once used for pantothenic acid and sometimes, incorrectly, used for niacin. vitamin B4 Name given to what was later identiﬁed as a mixture of the amino acids arginine, glycine and cystine. vitamin B5 Name given to a substance later presumed to be iden- tical with vitamin B6 or possibly nicotinic acid: also sometimes used for pantothenic acid. vitamin B6 Generic descriptor for three compounds (chemically derivatives of 2-methylpyridine): the hydroxyl (alcohol) com- pound, pyridoxine (previously known as adermin and pyridoxol); the aldehyde, pyridoxal; and the amine, pyridoxamine; and their phosphates. All are equally active biologically. The active metabolite is pyridoxal 5′-phosphate, which acts as a coenzyme in decarboxylation and transamination of amino acids, and in glycogen phosphorylase (EC 2.4.1.1), it also has a role in termi- nating the actions of steroid hormones. Deﬁciency causes abnormalities in the metabolism of the amino acids tryptophan and methionine; in rats convulsions and skin lesions (acrodynia) and in dairy cows and dogs, anaemia with abnormal red blood cells. Dietary deﬁciency leading to clin- ical signs is not known in human beings, apart from a single out- break in babies fed a severely overheated preparation of formula milk in the 1950s; they showed abnormalities of amino acid metabolism and convulsions resembling epileptic seizures, which responded to supplements of the vitamin. See also methionine load test; transaminase; tryptophan load test. VITAMIN B6 vitamin B6 dependency syndromes A very small number of chil- dren suffer from genetic diseases affecting the binding of pyridoxal phosphate to just one of the pyridoxal phosphate-
498 dependent enzymes. The abnormality is corrected by the admin- istration of large supplements of vitamin B6. vitamin B6 toxicity High intakes of supplements of vitamin B6, in excess of 200–1000 mg/day (far in excess of what could be obtained from foods) cause peripheral sensory neuropathy. vitamin B7, B8 and B9 In the early days of nutrition research, when a new factor was discovered that was claimed to be essential for chick growth and feathering, the claimant stated that since nine factors were known the new factors should be called vitamins B10 and B11. In fact, the B vitamins had been numbered only up to B6, hence B7, B8 and B9 have never existed. B9 is sometimes (incorrectly) used for folic acid. vitamin B10 and B11 The names given to two factors claimed to be essential for chick growth and feathering; they were later shown to be a mixture of vitamin B1 and folic acid. vitamin B12 (see p. 499) Cobalamin; coenzyme for methionine synthetase (EC 2.1.1.13, important in metabolism of folic acid), methylmalonyl CoA mutase (EC 5.4.99.2) and leucine aminomu- tase (EC 5.4.3.7). Deﬁciency leads to pernicious anaemia when immature red blood cells are released into the bloodstream, and there is degen- eration of the spinal cord. The anaemia is the same as seen in folate deﬁciency, and is due to impairment of folate metabolism. There is also urinary excretion of methylmalonic acid. Absorption of vitamin B12 requires intrinsic factor, a protein secreted in the gastric juice. Failure of absorption, rather than dietary deﬁciency, is the main cause of pernicious anaemia. However, B12 is found only in animal foods so strict vegetarians are at risk. See also dump suppression test; methyl folate trap; schilling test. vitamin B13 Orotic acid, an intermediate in pyrimidine synthesis; no evidence that it is a dietary essential; not a vitamin. vitamin B14 Not an established vitamin; name originally given to a compound found in human urine that increases the rate of cell proliferation in bone marrow culture. vitamin B15 pangamic acid; no evidence that it has any physio- logical function in the body; not a vitamin. vitamin B16 This term has never been used. vitamin B17 amygdalin (laetrile); no evidence that it has any physiological function in the body; not a vitamin. vitamin BC Obsolete name for folic acid. vitamin BD Called the antiperosis factor for chicks, but can be replaced by manganese and choline (not a dietary essential for human beings).
499 VITAMIN B12 vitamin BT carnitine; an essential dietary factor for the meal- worm Tenebrio molitor, and certain related species, but not a dietary essential for human beings. vitamin BW Or factor W; probably identical to biotin. vitamin BX Non-existent; has been used in the past for both pantothenic acid and PARA-amino benzoic acid. vitamin C ascorbic acid. For formula, see p. 39. It functions as a cofactor for a group of hydroxylases that also catalyse the decarboxylation of 2-oxoglutarate (including the hydroxylation of lysine and proline in the synthesis of collagen, and two hydroxylases in the synthesis of carnitine); in these reactions it is consumed, but not stoichiometrically with substrates. It is also the coenzyme for dopamine β-hydroxylase (EC 1.14.17.1) in the
500 synthesis of noradrenaline, and peptidyl glycine hydroxylase (EC 1.14.17.3) in the post-synthetic modiﬁcation of a number of peptide hormones. It is a general (non-enzymic) antioxidant, including the reduction of oxidised vitamin e in cell membranes. Deﬁciency results in scurvy: seepage of blood from capillar- ies, subcutaneous bleeding, weakness of muscles, soft, spongy gums and loss of dental cement, leading to loss of teeth and in advanced cases deep bone pain. A lesser degree of deﬁciency results in impaired healing of wounds. The requirement to prevent scurvy is less than 10 mg/day; ref- erence intakes range between 30 and 85 mg/day, depending on the criteria of adequacy adopted and the assumptions made in the interpretation of experimental data. At intakes above 100 mg/day the vitamin is excreted in the urine; there is no evidence of any adverse effects at intakes up to 4000 mg/day. Fruits and vegetables are rich sources; also used in curing ham, and as an antioxidant and bread improver. See also dichlorophenol indophenol; erythorbic acid; iron; o-phenylene diamine; oxalic acid. vitamin D (see p. 501) Vitamin D3 is calciol or cholecalciferol; formed in the skin by the action of ultraviolet light on 7-dehy- drocholesterol, hence not strictly a vitamin. However, in north- ern latitudes sunlight exposure may not be adequate to meet requirements, and a dietary source becomes essential. Vitamin D2 (ercalciol or ergocalciferol) is a synthetic vitamer produced by irradiation of ergosterol. The name vitamin D1 was given originally to an impure mixture and is not used now. The main storage form of the vitamin is the 25-hydroxy derivative, calcidiol, in plasma; the active metabolite is the 1,25-dihydroxy derivative, calcitriol. Formation of calcitriol is regulated by the state of calcium balance. The function of calcitriol is mainly in regulation of calcium metabolism; it acts via nuclear receptors, like a steroid hormone, and also via cell-surface receptors. Stimulates absorption of dietary calcium from the small intestine and calcium turnover in bone, by activating osteoblasts to mobilise calcium, then later recruiting and stimulating differentiation of osteoblast precur- sors for bone formation. Acting to regulate intracellular calcium concentrations, it is important in control of the secretion of insulin and other hormones. It also has a role (together with vitamin a) in regulation of cell differentiation and replication, and control of the cell cycle. Deﬁciency causes rickets in young children, osteomalacia in adults. Not widely distributed in foods; egg yolk, butter, oily ﬁsh and enriched margarine are the only signiﬁcant sources. Reference
501 VITAMIN D intakes are 10–15 µg/day for adults, amounts that are unlikely to be obtained from unsupplemented diets. The obsolete international unit of vitamin D = 25 ng calciol; 1 mg calciol = 40 IU. vitamin D resistant rickets See rickets. vitamin D toxicity Excessive intake of vitamin D results in dis- turbance of calcium metabolism, resulting in hypercalcaemia, dangerously raised blood calcium concentrations, leading to raised blood pressure, and calcinosis, inappropriate deposition of calcium in soft tissues, leading to brain and kidney damage. Excessive exposure to sunlight does not lead to excessive for- mation of vitamin D because previtamin D undergoes further light-catalysed reactions to inactive compounds, and there is only limited availability of 7-dehydrocholesterol in the skin. vitamin E (see p. 502) Two main groups of compounds have vitamin E activity: the tocopherols and the tocotrienols; there are four isomers of each: α-, β-, γ- and δ-tocopherols and α-, β-, γ- and δ-tocotrienols, with differing potencies. Deﬁciency symptoms vary considerably in different animal species; sterility in mouse, rat, rabbit, sheep and turkey; muscu- lar dystrophy in several species; capillary permeability in chick and turkey; anaemia in monkey. Human dietary deﬁciency is unknown, but hereditary lack of β-lipoprotein leads to functional deﬁciency, with severe neurological damage. Premature infants may show haemolytic anaemia as a result of vitamin E deﬁciency. Functions as an antioxidant in cell membranes, protecting unsaturated fatty acids from oxidative damage. It also has membrane-speciﬁc functions, and a role in cell signalling and modulation of gene expression. The vitamin E content of foods is expressed as milligrams α- tocopherol equivalent (based on the different potency of the dif- ferent vitamers). The obsolete international unit of vitamin E
502 VITAMIN E activity was equal to 1 mg of synthetic α-tocopherol; on this basis natural source α-tocopherol is 1.49 IU/mg. vitamin F Sometimes used for the essential fatty acids. vitamin G Obsolete name for vitamin b2.
503 vitamin H See biotin. vitamin K Two groups of compounds have vitamin K activity: phylloquinones (vitamin K1), found in all green plants, and a variety of menaquinone (vitamin K2) synthesised by intestinal bacteria. Vitamin K3 is a synthetic analogue, menadione. Functions as coenzyme in carboxylation of glutamate to γ- carboxyglutamate in a number of calcium binding proteins, including prothrombin and other proteins involved in the blood clotting system, the bone protein osteocalcin, and the product of the growth arrest-speciﬁc gene (Gas-6), which is important in regulation of growth and development. Dietary deﬁciency is unknown, except associated with general malabsorption diseases. However, some newborn infants are at risk of developing haemorrhagic disease as a result of low vitamin K status, and it is general practice to give a single rela- tively large dose of the vitamin by injection. See also anticoagulants; dicoumarol; warfarin. VITAMIN K vitamin L Factors extracted from yeast and thought at the time to be essential for lactation; they have not become established vitamins. vitamin M Obsolete name for folic acid. vitaminoids Name given to compounds with ‘vitamin-like’ activ- ity; considered by some to be vitamins or partially to replace vitamins. Include ﬂavonoids (vitamin p), inositol, carnitine, choline, lipoic acid and the essential fatty acids (see fatty acids,
504 essential). With the exception of the essential fatty acids, there is no evidence that any of them is a dietary essential. vitamin P Name given to a group of plant ﬂavonoids (sometimes called bioﬂavonoids) that affect the strength of blood capillaries: rutin (in buckwheat), hesperidin, eriodictin and citrin (a mixture of hesperidin and eriodictin in the pith of citrus fruits). Now considered that the effect is pharmacological and that they are not dietary essentials, although they have antioxidant activity. Called vitamin P from the German permeabilitäts vitamin, because of the effect on capillary permeability and fragility. vitamin PP The pellagra-preventing vitamin, an old name for niacin before it was identiﬁed. vitamin Q See ubiquinone. vitamin T Factor found in insect cuticle, mould mycelia and yeast fermentation liquor, claimed to accelerate maturation and promote protein synthesis. Also known as torulitine. Said to be a mixture of folic acid, vitamin B12 and deoxyribosides (DNA); hence not a particular vitamin. vitellin The major protein of egg yolk; approximately 80% of the total; a phosphoprotein accounting for 30% of the phosphorus of egg yolk. VLDL Very low-density lipoprotein, see lipoproteins, plasma. VOC Volatile organic compounds vodka Made from neutral spirit, i.e. alcohol distillate mainly from potatoes, with little or no acid, so that there is no ester forma- tion and hence no ﬂavour. Polish vodka is ﬂavoured with a variety of herbs and fruits. voidage The fraction of the total volume occupied by air (the degree of openness) of a bed of material in ﬂuidised-bed drying. VolTM Commercial ammonium carbonate, a mixture of ammo- nium bicarbonate and carbamate. Used as aerating agent in baking, as it breaks down to carbon dioxide, ammonia and steam on heating, without leaving any residue. volvulus Twisting of part of the gastrointestinal tract, leading to partial or complete obstruction. votator Machine used for the continuous manufacture of mar- garine; the fat and water are emulsiﬁed, and the subsequent conditioning process carried out in the same machine. VP Vacuum packaging. VSP Vacuum skin packaging. W wähe Swiss; tarts made from yeast-leavened dough ﬁlled with fruit, vegetables or cheese. waist : hip circumference ratio Simple method for describing the